Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $245.93   9.367%   $268.9663   $268.97   $268.95   $269.00  
  Purchase #2 $232.90   9.208%   $254.3454   $254.35   $254.35   $254.30  
  Purchase #3 $95.26   9.482%   $104.2926   $104.29   $104.30   $104.30  
  Purchase #4 $25.55   9.798%   $28.0534   $28.05   $28.05   $28.10  
  Purchase #5 $248.67   5.384%   $262.0584   $262.06   $262.05   $262.10  
  Purchase #6 $183.76   10.294%   $202.6763   $202.68   $202.70   $202.70  
  Purchase #7 $149.58   6.538%   $159.3595   $159.36   $159.35   $159.40  
  7 purchase totals = $1,181.65       $1,279.7519   $1,279.76   $1,279.75   $1,279.90